Heat resistant resins such as polyimides, polybenzoxazoles, and the like have been widely used to form an interlayer insulating layer and/or a planarization layer for a display device such as an organic light emitting diode (OLED), liquid crystal display (LCD), and the like. In particular, heat resistant photosensitive polyimides and photosensitive polybenzoxazoles have recently been used to form an interlayer insulating layer and the like in an OLED in order to secure reliability of the OLED.
The photosensitive polyimide and polybenzoxazole can have excellent physical characteristics such as heat resistance, mechanical strength and the like, excellent electrical characteristics such as a low dielectric constant, a high insulation property, and the like, good planarization characteristics on a coating surface, include very small amounts of impurities that can deteriorate reliability of a device, and easily form a fine shape.
On the other hand, when the heat resistant resin is used to form the insulation layer, the planarization layer, or the like for an organic light emitting diode, a substrate on which the resin is coated is larger than the one used for a semiconductor, and spin-coating used for the semiconductor may not be adopted. Accordingly, slit-coating is generally adopted to coat the resin composition and form the insulation layer or planarization layer for an organic light emitting diode.
The slit coating is performed by using a slit nozzle and is applicable to a large substrate having a large area. Slit coating does not require spinning the substrate and thus decreases the amount of the resin composition compared with the conventional spin-coating. Slit coating is appropriately used for manufacturing a display device.
When a coating liquid ejected from the slit nozzle during the slit coating is coated on the substrate, the coated layer includes a large amount of a solvent and thus, is generally heated and dried on a hot plate and the like after removing the solvent at room temperature under a reduced pressure. Accordingly, it is important to select an appropriate solvent for the slit coating in preparation of the photosensitive resin composition including a polyimide precursor or a polybenzoxazole precursor and a photo sensitizer and used to form the insulation layer, planarization layer, and the like for an organic light emitting diode.